Tuberous sclerosis complex (TSC) is a genetically inherited disease of benign tumors in multiple organs. Loss or inactivation of the TSC1 or TSC2 tumor suppressor genes leads to abnormally high activity of the protein mammalian target of rapamycin (mTOR), and excessive cell growth. Arising in one third of patients with tuberous sclerosis complex, lymphangioleiomyomatosis (LAM) features abnormal proliferation of neoplastic smooth muscle-like cells (LAM cells) that leads to cystic destruction of the lung, progressive respiratory failure, and lung transplantation or death. Our long-term goal is to better understand the molecular pathogenesis of tuberous sclerosis complex and LAM. The current therapeutic approach for the treatment of TSC and LAM is to block mTOR activity and cell proliferation. However, mTOR can control a variety of other cellular functions that depend on its presence in distinct macromolecular protein complexes, as well as its cellular location. Our group recently discovered a new mTOR complex that is induced by interferon-(, and contains proteins involved in apoptosis. These include the transcription factor 'signal transducer and activator of transcription-1 (STAT1) and protein kinase C-delta. We propose to investigate the molecular mechanisms that regulate mTOR/STAT1 complex assembly and cellular trafficking, because these events are likely to favor the death of LAM cells, and represent a complementary therapeutic strategy. The specific aims of this proposal are: 1) To determine the biochemical requirements for mTOR/STAT1 protein-protein interactions, 2) To define the nature and requirements for cellular trafficking of the mTOR/ STAT1 complex, 3) To investigate the role of STAT1, and its physical interactions with mTOR, in the control of proliferation and apoptosis in LAM cells, a model of cellular TSC2 deficiency. To examine the molecular requirements for the assembly and cellular trafficking of the mTOR /STAT1 complex, we will employ complementary protein purification techniques, in vitro assays with recombinant proteins, and advanced imaging techniques. Finally, we will investigate the role of mTOR/STAT1 signaling in LAM cell cultures, and biopsy specimens from patients with tuberous sclerosis complex and LAM. Results from these studies will establish a role for rnTOR/STAT1 signaling in the cellular pathophysiology of LAM and tuberous sclerosis, as well as efficient experimental models and platforms to identify novel therapeutic agents.